Humans and many other animals can estimate rapidly and reasonably accurately the number of items in the scene. Neurophysiological studies on human and non-human primates point to the existence of a dedicated numbersense, served by specialized neural mechanisms in parietal and prefrontal cortex. Over a wide range of conditions, humans discriminate number spontaneously and directly, relatively unconfounded by related attributes such as texture-density. Like other sensory attributes, the numbersense is selectively adaptable. Cross-modal and cross-format adaptation studies show that the number sense is general, transgressing space, time and sensory modality, and closely linked with the preparation of action. Taken together, the sense of number can be considered a perceptual quale.